The present invention relates to drawing tubes or pipes, and more particularly, the invention relates to drawing hollows in several stages or steps while supporting the hollow from the inside.
It is known generally to draw tubes or pipes by means of an annular die while supporting the tube or pipe on an inserted mandrel. The hollow blank is drawn and stretched in this fashion onto and over the mandrel. However, the deformability (ductility) of the hollow blank is limited on account of its structural properties. For larger degrees of deforming and working one has to draw the blank in sequential steps. The known equipment is quite extensive and the working time is multiplied. The same drawbacks can be observed upon inside drawing the blank. The known multiple drawing techniques in particular involve annealing, repickling and bonderizing the partially blank drawn between drawing steps; also new bottle-necking has to be provided for.